1. Field of the Invention
This invention relates to the switching and routing of optical signals for telecommunications and optical computing applications. More particularly, the invention relates to an array of polarizing reflectors and programmable phase retarders arranged to couple N optical input signals to any combination of N output locations.
2. Background Information
Throughout this application, various publications, patents and patent applications are referred to by an identifying citation. The disclosures of the publications, patents and patent applications referenced in this application are hereby incorporated by reference into the present disclosure.
High-speed optical interconnections promise to play a major role in the development of national and global information infrastructure, as applications such as super-computing, telecommunications switching and military C.sup.3 I rely on the ability to route data at increasingly high bit rates. Research and development of high-bit-rate optical switches has been pursued worldwide. The Japanese government has funded research on multi-gigabit-per-second optical switches, and Toshiba Corporation has demonstrated a 155 MBIT per-second 64.times.64 ATM switch. Such throughput is sufficient for many of today's applications, and is comparable to the performance that may be achieved using electronic switching. However, the electronics required to implement these switches becomes particularly difficult as the number (N) of input/output ports increases, i.e. as N approaches or exceeds 64. In addition, the relatively large bandwidth of optical fibers (generally three orders of magnitude greater than that of similar diameter coaxial cables) has not been fully exploited due to the lack of all-optical switches capable of routing terabit-per-second data streams.
Some of the most commonly utilized interconnects in fiber-optic networks are optoelectronic devices. These switches convert optical input signals to electrical signals by use of a photodetector/preamplifier/amplifier array. These converted signals are then typically routed electronically to a diode laser array which regenerates the optical signals. Because the routing is performed electronically, the channel bandwidth in this technique is limited by the bandwidth of the switching electronics, which in theory may approach 620 MHZ, but tends to be on the order of 150-200 MHZ. In addition, once the optical signal is converted into an electronic signal, it becomes susceptible to electrical crosstalk, electromagnetic interference (EMI) noise, and transmission line-type propagation delays.
To overcome these bandwidth limitations, several all-optical switches have been designed and are commercially available. These devices do not require conversion of the optical signal, and are therefore able to accommodate relatively high data rates. Being free from the bandwidth limitations of conventional electronic devices, such all-optical switches may accommodate terabit-per-second data streams to avoid being a bottleneck in all-fiber-optic networks. The approaches utilized to provide such devices are varied, most including mechanical and/or polarization based techniques.
One example of such a device, includes an interconnect available from Optivision, Inc., of Palo Alto, Calif. This device utilizes semiconductor optical amplifiers (SOA'S) in a matrix-vector architecture to achieve high speed switching. This system, however, requires optical amplification to compensate for internal losses, is relatively bulky, and is limited to eight I/O ports.
An example of an opto-mechanical optical interconnect is commercially available from Astarte Networks, Inc. In operation, light from each input fiber is collimated with a lens and is steered to its proper destination with a piezoelectrically-activated mirror. At the output ports, the light is coupled into fibers by use of another set of lenses. While this device exhibits a relatively large (free-space) bandwidth, its mechanical nature introduces several significant drawbacks. One drawback of such a mechanical device is its relatively slow reconfiguration time, of approximately 50 ms. In addition, use of piezoelectrically activated mirrors tends to make this switch particularly susceptible to mechanical perturbations, vibrations, etc. These limitations may be somewhat alleviated by a system of tracking servos, however such a stabilization system disadvantageously tends to be relatively complex.
Polarization based switches operate by use of polarization gates. Such devices tend to be robust, mechanically stable, and may achieve microsecond (or faster) reconfiguration times. These devices, however, have been based on relatively cumbersome network architectures, making them impractical and difficult to scale to a system with a relatively high number of I/O ports. Moreover, these devices have unequal pathlengths between various I/O ports thus exhibiting non-constant latency, differing levels of signal attenuation and a skewed output data stream. Thus, a need exists for a high-speed, compact, high-capacity, and robust all-optical interconnect device having a constant signal pathlength for all I/O permutations.